ABS (anti-lock braking systems) prevent the wheels from locking, and perform their function if greater traction is demanded between a tire and the roadway than can be transmitted, that is to say if the driver overbrakes. In the event of overbraking, the central electronic control unit of the ABS brake system detects, from rotational speed sensor signals, a tendency of one or more wheels to lock, and from this calculates the activation of the pressure control valve arrangement acting on the associated brake cylinders. The brake pressure is then adjusted, by being lowered, held or built up, by the pressure control valve arrangement as a function of the wheel behavior, and the friction conditions between the tire and roadway are thereby set to an optimum level of slip.
ABS pressure control valve arrangements without a relay action are used in vehicles such as for example utility vehicles, omnibuses, semitrailer tractors and also in trailers. Pressure control valve arrangements without a relay action generally have 3/2 directional control solenoid valves as pilot control valves of diaphragm valves, wherein an electronic control device activates the 3/2 directional control solenoid valves so as to be able to carry out the “pressure holding”, “pressure dissipation” and “pressure build-up” functions required for ABS operation. During a braking operation without ABS response (no tendency of a wheel to lock), the pressure medium, usually air, flows through the pressure control valve arrangements unhindered in both directions during the aeration and deaeration of the brake cylinders. It is thereby ensured that the function of the service brake system is not influenced by the ABS pressure control valve arrangement.
Pressure control valves of the generic type as single-duct pressure control valves for anti-lock systems of motor vehicles have, within the housing, in each case one diaphragm valve as a holding valve and as an outlet valve, and in each case one electromagnetic control valve for the holding valve and the outlet valve. The two diaphragm valves comprise in each case one diaphragm which can be acted on with the pressure in a control chamber, wherein the control chamber is closed off to the outside by a cover fastened to the housing.
A generic pressure control valve arrangement of an ABS brake system is discussed for example in EP 0 266 555 A1. In the pressure control valve arrangements of the prior art, the two diaphragm valves are usually arranged on the side of the housing, wherein the corresponding pilot control chambers are closed off by covers fastened to the side of the housing. The covers are produced by primary forming processes such as injection molding. Furthermore, pressure medium ducts are formed in the housing in order to conduct pressure medium within the housing from and to the various ports of the pressure control valve and to and from the diaphragm valves and from and to the electromagnetic valves which control the diaphragm valves.
The pressure medium ducts in the housing of the pressure control valve arrangement according to EP 0 266 555 A1 are manufactured in a cutting process and may be run in a vertical and/or horizontal direction, because then it is not necessary for the housing to be re-clamped during the cutting manufacturing of the pressure medium ducts, for example by a machining center. A diversion of a pressure medium duct is thus realized in that in each case one vertical and one horizontal bore overlap. A problem from a flow aspect is a resulting diversion of a pressure medium duct, because the diversion takes place abruptly in the intersection region between the vertical bore and the horizontal bore, and relatively large flow losses arise as a result of the abrupt diversion. However, because high dynamics are demanded of pressure control valve arrangements of ABS/ASR systems, and for example during the course of the “pressure reduction” function in the event of an exceedance of the admissible wheel slip as fast as possible a deaeration of the relevant brake cylinder is demanded, such flow losses caused by diversions must be kept as small as possible.
Because the installation dimensions, in particular the installation width, of a pressure control valve arrangement of the type are standardized and cannot be varied owing to restricted spatial conditions, a solution to the problem cannot involve the enlargement of the flow cross sections of the pressure medium ducts.